1.Field of the Invention
The present invention relates to a water pump to be used for circulating a coolant for an internal combustion engine of an automotive vehicle, or so forth. More particularly, the invention relates to a water pump and a manufacturing method of the water pump, in which an intermediate portion of a rotary shaft is supported by a bearing fitted on a boss portion of a housing, a rotary body, such as a pulley, is fixedly mounted on one end portion of the rotary shaft extending from the bearing, a pump impeller is rigidly fixed on the other end of the rotary shaft extending toward a swirl chamber of the housing, and a mechanical seal is disposed between the pump impeller and the bearing.
2. Description of the Related Art
A conventional water pump is constructed as shown in FIG. 1. A rotary shaft 1 of the water pump is supported on a pump housing 3 via a bearing 2. On a tip end of the rotary shaft 1, a pump impeller 4 is rigidly fixed. On the other hand, on a base end portion of the rotary shaft 1, a pulley hub 5 is rigidly fixed. Between the bearing 2 and the pump impeller 4, a mechanical seal 6, which is constituted of a stationary member 6a fixed on the side of the housing 3 and a rotary member 6b fixedly engaged with the rotary shaft 1, is disposed in a condition where both of the members 6a and 6b are abutted with each other by biasing sliding members thereof by means of springs. The reference numeral 7 denotes a lid body forming a swirl chamber 8 located in opposition to the pump impeller 4. The lid body 7 is fixed to the pump housing 3 by means of fastening bolts 9. While not illustrated, a suction portion and a discharge port are provided in the lid body 7.
When a temperature of an engine coolant circulated by the water pump is elevated during the use of such type of the water pump, a small amount of moisture in a form of vapor can pass through the mechanical seal 6 from the swirl chamber 8 toward the bearing 2. Such moisture can cause fatigue of a seal rubber provided on the end portion on the side of the mechanical seal of the bearing 2 or can damage the bearing.
As a solution for the problems set forth above, Japanese Unexamined Patent Publication No. Hei 8-338535 proposes a construction, in which two seal rings are proposed in parallel in spaced apart relationship, a lubricant is filled between these seal rings, and the seal ring on the side of the swirl chamber is slidable in an axial direction for establishing a balance between a pressurized water and the lubricant. Furthermore, Japanese Unexamined Patent Publication No. Hei 9-88886 proposes a construction, in which an annular sealing lip varying depression force onto the rotary shaft depending upon a pressure on the side of the swirl chamber, is disposed between the bearing and the swirl chamber.
However, in case of the former, it is inherently required that one of the sealing members is movable depending upon the pressure within the swirl chamber to make the construction and treatment troublesome to cause higher cost. Furthermore, in the latter case, a sealing effect cannot be achieved unless the pressure within the swirl chamber becomes higher than, or equal to, a predetermined value. Therefore, a problem is encountered in a sealing ability.